Overview
ISO 21452:2025 - Specification and requirements of thermal spray coatings for power plant boiler tubes - provides standardized procedures and performance requirements for applying thermal-sprayed coatings to water walls and superheaters in coal-fired and biomass boilers. The standard covers selection of coating materials, substrate preparation for 12/15CrMoV steel, pre-treatment, thermal spraying and post-treatment (including sealing and heat treatment), plus coating quality and performance evaluation.
Key topics and requirements
- Scope: Coatings for water wall and superheater tubes in coal-fired and biomass boilers; focuses on corrosion, wear, coking and fatigue mitigation.
- Recommended coating materials: Examples include NiCrTi, NiCr–CrC, FeCrBMoC, NiCrBSi and NiCrMoNb matched to failure modes and tube types.
- Substrate and pre-treatment:
- Surface cleaning: alkali washing and acid pickling (procedures provided) to remove grease, scale and weld impurities.
- Surface roughening: dry sandblasting with specified abrasive grain sizes and target roughness (Ra ~5.4–6.0 µm); controlled blast pressures and storage time prior to spraying.
- Thermal spraying process controls:
- Follow ISO 14918 / ISO 14921 practices for sprayer qualification and process.
- Spray sequencing (edges/arcs first), gun motion guidance, and substrate temperature limits (not to exceed 200 °C; cool to ≤80 °C if needed).
- Post-processing:
- Sealing of pores immediately after spraying; sealants rated for high temperature (400–600 °C).
- Inspection for thickness, roughness, microhardness and bond strength.
- Performance metrics and testing:
- Defined performance indicators such as microhardness, porosity, thermal conductivity, hot-corrosion kinetics and erosive wear rates with recommended ranges by tube type.
- Test methods referenced: Vickers microhardness (ISO 6507-1), bond strength (ISO 14916), and other evaluation methods.
Applications and users
- Who uses ISO 21452:2025:
- Power plant engineers and boiler maintenance teams
- Thermal spray contractors and coating suppliers
- Boiler manufacturers, plant reliability and asset managers
- Test laboratories and certification bodies
- Practical value:
- Extends tube service life and reduces unplanned outages by selecting appropriate coatings and process controls
- Provides measurable acceptance criteria for coating quality and in-service performance
- Enables consistent supplier qualification and coating verification across the power generation sector
Related standards
Keywords: ISO 21452:2025, thermal spray coatings, boiler tubes, power plant, 12/15CrMoV steel, water wall, superheater, coating quality, hot corrosion, erosion resistance.
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